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Old 12-08-2016, 07:42 AM
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Crushellon (Tim)
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GSO CF RC8 or Skywatcher CF f4 Newt

Cant decide which scope to go for. Other than different focal lengths and speeds has anyone got any opinions on these two scopes ie: build quality and ease of installing a heater on the secondary. There's an rc8 on the forums at the moment with a moonlite focuser for $1200...
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Old 12-08-2016, 08:34 AM
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alocky (Andrew lockwood)
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The main factors will be the type of camera you intend to use and the image scale you are hoping for. The newt will need a coma corrector for imaging at f4, but for the same image scale you can use a smaller sensor and much cheaper filters to get fairly similar results. For the cost of an rc8 you can probably get a larger fast newt, too... For visual, the newt would probably be better, although there's not likely to be much in it.
Cheers,
Andrew.
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Old 12-08-2016, 08:40 AM
glend (Glen)
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Go with the Newt. I had a GSO RC08 and it drove me crazy; you need to have extreme patience with them but they can produce great results. They do not come supplied with focuser collimation rings and these are necessary for focuser alignment. Sure you can stick a Moonlight on it, but without the focuser collimation ring (an extra $100) you would be messing up the rotation ability of the Moonlight if you tried to adjust it in a fixed position to the secondary centre spot. Most people wind up buying extra collimation aids for the RC like the Tak Collimation scope (add another $230 or so for that), or a Howie Glatter Concentric Ring laser.
Newts, for most people are much easier to live with.
Of course the RC will give you long focal length that the f4 Newt will not. You could consider an f5 newt, and the GSO ones are fine and good imaging scopes, at a wonderful price. On an NEQ6, the GSO 10" f5 Newt might be a tad heavy for imaging depending on your camera imaging train setup.
Get a Baader MPCC MarkIII Coma Corrector, a magic device.
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Old 12-08-2016, 09:24 AM
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Crushellon (Tim)
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I have a baader mpcciii for my current scope and I'm getting an asi1600. One of the main considerations for me is a readily available secondary heater because as I found out with my first trip to a dark site last week I won't get much imaging done without one. I'm pretty comfortable with using/collimating a newt now but I like the image quality and focal length of the rc's.

If I went for the newt it would be the 10" cf f4 from Skywatcher, cause it's light enough for the mount.
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Old 12-08-2016, 10:27 AM
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jjjnettie (Jeanette)
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I'm pretty sure the RC8 has a secondary heater installed.
I have to take more pics when I go pick it up.
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Old 12-08-2016, 11:49 AM
glend (Glen)
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Ok Tim, just trying to help. Collimating an RC is nothing like collimating a Newt.
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Old 12-08-2016, 12:00 PM
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jjjnettie (Jeanette)
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The trick is knowing that you only should adjust the secondary. Leave the primary alone!!!!
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Old 12-08-2016, 12:09 PM
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Crushellon (Tim)
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Quote:
Originally Posted by glend View Post
Ok Tim, just trying to help. Collimating an RC is nothing like collimating a Newt.
Thanks,I appreciate it. I didn't even know collimating them was a big deal, I have no idea at all about using an RC. I just meant that the fact that I'm comfortable with a reflector is one of the pros for staying with a newt.
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Old 12-08-2016, 12:09 PM
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Hi Tim

The rc8 with that moonlight is a bargain. Here is also one up from David Naskies which is a steal as well. Check out some of the images he was churning out with it.

What I like about mine is that it has a huge amount of back focus and the moonlight handles the imaging train well ( stl603 and mmoag)

With the as1600 chip you won't see too much of the curvature you get with an RC because of the mirror design as well. I don't use a flattener and just crop away any issues.

collimation is fun but once dialed in you don't need to adjust much, well, when you have a permanent setup that is. Tweaking with the secondary gets you where you need to be, you should very rarely need to adjust the primary Search ICE for Als collimating aide as well. Great for tweaking the secondary.

Focus holds very well during the night.

If you did want to throw a little extra money at the scope, the tak collimater plus adapters makes life easy as does the GSO tilt ring. I don't use laser gadgets

Will be fine on an eq6.

Of course it's slower than the newt but that's just a question what you want to image and then just Patience.
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Old 12-08-2016, 07:42 PM
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Quote:
Originally Posted by Crushellon View Post
I have a baader mpcciii for my current scope and I'm getting an asi1600. One of the main considerations for me is a readily available secondary heater because as I found out with my first trip to a dark site last week I won't get much imaging done without one. I'm pretty comfortable with using/collimating a newt now but I like the image quality and focal length of the rc's.

If I went for the newt it would be the 10" cf f4 from Skywatcher, cause it's light enough for the mount.
I retrofitted a secondary heater to my 10" newt, and it was very straightforward- but, at 3.8 micron pixels that camera is not a great match for the rc8, and is almost over sampling a 10".
Cheers,
Andrew.
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Old 13-08-2016, 10:10 AM
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lazjen (Chris)
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Binning and/or a reducer would make the scopes match better to the camera, right?
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Old 13-08-2016, 12:42 PM
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Originally Posted by lazjen View Post
Binning and/or a reducer would make the scopes match better to the camera, right?
Sure - avoiding binning though because it seems a waste,
At f8 an rc8 with that camera will give 0.49 arc secs/ pixel which is a bit ambitious without adaptive optics (ESO style, not amateur). A 0.8 reducer gives you .61 which is starting to be more realistic especially if you have good seeing, but still a bit optimistic.
A 10" f4 will get .78 "/px which would be perfect.
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Old 13-08-2016, 01:48 PM
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lazjen (Chris)
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I'm not sure if it would work with the RC8, but I can get a 0.67 FR working with my RC10. For the RC8, if it works, you'd get 0.72 arc secs/pixel.
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Old 13-08-2016, 04:28 PM
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So I ended up going with the rc8.... I got a pretty good deal on the rc8 & an ed80 both with moonlites and a moonlite controller, an 0.85x Skywatcher reducer/corrector, heat straps for the whole lot and a dual channel dew controller. Haven't got the camera yet so I'm still open on that one, but really though for a cooled camera at $1600 is it really that bad a match? I have to consider that I will be using it with both rc8 & ed80 now that I have both scopes. (Wasn't really in the market for an ed80, but I couldn't pass up a good deal)
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Old 13-08-2016, 07:39 PM
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Have a read of this page (http://astronomy.tools/calculators/ccd_suitability) and use the calculator at the end. Plug in your scope and camera, with / without the reducer and see the results.

If you do that, you'll see that you're probably going to be oversampling with the ASI1600, which is not ideal.

If you had a 0.67 reducer and it worked for focus, etc, then the ASI1600 would be fine.

Last edited by lazjen; 13-08-2016 at 07:39 PM. Reason: missing link :)
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Old 13-08-2016, 08:36 PM
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Crushellon (Tim)
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Not really keen on going for a reducer, kind of defeats the purpose of the scope if I'm just gonna bring it back to ~1000mm focal length. So why is binning a bad idea? I figure the camera is a good match for the ed80 at 1x1 and good for the rc8 at 2x2? If I got a camera with bigger pixels Id be under sampling with the ed80 which is really bad as I understand it (which I don't btw)
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Old 13-08-2016, 09:55 PM
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Hi Tim

I found this article useful when trying to get my head around this. There is an excellent diagram showing the relationship between focal length and pixel size.
http://www.skyandtelescope.com/astro...-reducers/?c=y

There is an sbig stf8300 in classifieds that might be a better fit for you?
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Old 13-08-2016, 11:03 PM
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I'm going for an osc camera, so the sbig is no good.
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Old 14-08-2016, 10:53 AM
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Atmos (Colin)
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You could always just get another astro modified DSLR. Central DS have quite a nice range of cooled DSLRs. Many of those are likely to have larger pixels that the ASI1600. All depends on budget though I suppose.
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Old 14-08-2016, 11:33 AM
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Sampling at 0.49"/px is going to be pretty tough. Going by the 3x rule of thumb, that means the total of your guiding error, optics and seeing would want to be about 1.5" for you to be appropriately sampled. Not undoable, but you need a good mount and good seeing. Even with a reducer bringing it down to 0.61"/px it's not going to be easy. Either you need low expectations, or a seriously good mount and good skies.

I also would not bin the ASI 1600. It drops back to 10 bit mode and according to the manufacturer, the only real benefit you get to binning the 1600 is reducing the file size.

If you dither and use drizzle integration, you can "get back" some of that lost resolution on one of those rare nights that everything falls into place and you end up undersampled.
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